单项选择题
A spherical buoy may be（）.
A.numbered B.lettered C.green D.red
单项选择题 A special purpose buoy shall be（）.
单项选择题 A special mark (yellow buoy)，if lighted，may exhibit which light rhythm?（）
单项选择题 A SEAMARK，I.E. A BUOY，INDICATING THE NORTH，EAST，SOUTH OR WEST FROM A FIXED POINT，E.G. A WRECK is（）.
